One page at a time, I'm reviewing Sapiens: A Brief History of Humankind by Yuval Noah Harari.
Page 5
Please forgive the breakfast crumb. After brushing it off, I thought to re-take the photo, until it occurred to me that this really is a crummy page.
Smack in the middle, there's a mind-blowing bit, the kind that gives you that numinous feeling, or something like it, that I'm going to have to ruin. And it's not going to be easy. If he hadn't written it in the first place, and if it wasn't the internationally best-selling book about human evolution over the last decade, then I wouldn't have to go to the trouble.
Here's the bit: "Just 6 million years ago, a single female ape had two daughters. One became the ancestor of all chimpanzees, the other is our own grandmother."
It sounds amazing and fresh because no one's ever said this before. Why haven't they? Well, it's not because it took a great scientist or a great writer. No one has ever laid our origins so plainly like this before because it's not true.
It is true that genome-based estimates for our lineage's divergence from that which led to modern chimpanzees and bonobos (whom he never mentions and lumps entirely with chimpanzees) converge around 6-7 million years ago. And that's when we like to say our "last common ancestor" with chimpanzees and bonobos lived and died on planet Earth.
To see that estimate of 6-7 for yourself, just type human and chimpanzee into this site: https://timetree.org/
(Word to the wise, until the fad dies completely, you will get roaring laughter if you say something like the above in the lecture hall, and no one will tell you why until days later, and, upon hearing the reason, you will mentally pen your letter of resignation, but a moment later you will mentally wad up that letter and simply carry forward a small but mighty grudge against the students who refused to tell you what was so funny while you checked your fly was not down, or that your shirt was not up, or that a boog was not hanging.)
So, if Harari's amazing ape trio isn't true then what is?
Speciation takes time. That is, the separation of lineages is a process over time and space. No matter how drastic the beginnings of that separation, they always begin with populations. Apes today never live like Adam and Eve or like Harari's amazing ape trio. Lineages are always populations of individuals, or "gene pools" if you prefer.
And, sure, maybe one part of our genome compared to chimps' and bonobos' could be traced to one individual amazing ancient ape mama who birthed two different amazing kids (all mamas always do!), like, theoretically maybe that could be the story for one aspect of our (barely) distinct genomes.
But I never think about atomized individuals (who each have most but not all of their lineage's variation) in this context. I think about a group of apes who all together carry the whole genome of that phase of space-time for their lineage.
All that variation, which isn't much within a species, put together--that's what we're talking about when we talk about genomes. A bunch of individuals' genomes put together to make up the whole.
We have no idea how some individuals of our ancient ape ancestors separated off from one another, either genetically or physically or both, roughly 6-7 million years ago and we never will know how or why that happened. But it did. Using genomic data now, scientists have tried to estimate how long the divergence took. That is, they offer guesses for how many years went by before the genomes were as distinct as they are now. And it may have taken hundreds of thousands, or even millions of years. (For example, here's an old paper. And here are doubts about it.)
However slow or fast the divergence went, the genetic differences between us, chimps, and bonobos did not all appear all at once. And so, no we cannot trace what is genomically different between us and chimps/bonobos to one ancestor who had two kids that originated separate lineages. Like I said, I guess it's possible we could trace one aspect of our different genomes to one ancestor like that. But all our (puny amount of) differences all accumulated at different times and in different places. And, here's the extra complex part: All the differences accumulated, both, prior to full reproductive separation of our lineages, and ever since! There would have been gene flow during the speciation process, which, I think (but could be off) that some might call hybridization, depending on where in the process we're looking.
So, no, there is not one single ancient ape mother who birthed all chimps, bonobos, and humans and there is not one mother who started all chimpanzees or one mother who started all bonobos or one mother who started all humans. There is not even one ancient ape community or population, like in one single moment of space-time, that did. Speciation, or lineage separation, is an ongoing process. That 6-7 million-years-ago estimate is pointing at a phase in time, not a spot you could program into your flux capacitor.
Notice I said speciation is an ongoing process. We are still evolving in a different way from chimpanzees and bonobos and vice versa and vice versa (it's a three-way). Because we are not sharing any of our genetic material among our lineages through reproduction, then it's likely that we are all evolving to be more genetically different than one another, not more similar.
I was careful to include "genetically" as a modifer each time I wrote "different" because it is key to remember that our genetic differences and similarities are real and important but they are not the only similarities and differences! We may share 98-99% of our genomes with chimpanzees and bonobos but that does not mean we are 98-99% them any more than they are 98-99% us. That's because our genome is not determining everything about them or us. (Several pages from now, this will be an issue that I'm already girding my loins to revisit. Stay tuned.)
Refusing to reduce our origins like Harari and just trying to imagine reality is worthwhile because that's the really mind-blowing experience.
Sometimes, it's easier to over-simplify or to make something up entirely than to describe reality. Reality can be complicated and mysterious. I wish I could say that my attempt to tilt better at reality for you, as a replacement for Harari's made-up thing, was a brilliant reflection of reality's complexity and mystery. It's not hard to see why Harari's thing lives in a best-seller, though.
(For more on how to think about genetic variation in time and space, check out Graham Coop's Lab's blog and A Brief History of Everyone Who Ever Lived by Adam Rutherford.)
As far as the rest of this page goes, there are a couple more things to address.
Homo sapiens belongs to the ape family. Yes. Though, it's curios to read that it, "used to be one of history's most closely guarded secrets." Is he referring to history as an agent? Because I know of no conspiracy where actual humans concealed the truth of evolution. So he is referring to history as a thing separate from humans. I am THE WORST with metaphors, but I will try very hard to empathetically understand why he's doing this. Right. History guarded the secret of evolution. I'm trying very hard and... nope. I just don't get it. I think it must be his way of saying that it took a long time between the origins of complex human cognition for anyone to think evolutionarily. Right. (I mean, right, if you're restricting evolutionary thinking to European history. Indigenous knowledge can sound a heck of a lot like evolutionary thinking if you aren't stuck in the selfish gene metaphor!) Okay, fine. But the metaphor with history as an agent is still really strange for me.
I sure don't love being so critical about writing style (living in the glass house that I do). I only bring up this issue because the metaphor appears not once but twice on this same page:
"Homo sapiens has kept hidden an even more disturbing secret."
A whole species kept a secret?
I'm sorry. How can I be reading this for the ninth time and only now realizing how weird this page is? Or, rather, realizing how incapable I am of understanding its metaphors...
The big crummy problem above with the amazing ancient ape mama with two amazing kids (which might have been intended to be only a metaphor??? Oh god. What if it's only meant to be a metaphor and not science???) really sent me reeling. I think that's why, in all eight prior reads of this book, I didn't notice the rest of the page.
So what's this second secret that our entire species has been keeping? He's talking about how there were other species of hominins through time besides Homo sapiens. Why he needs to frame that fact as a "secret" that "sapiens has kept" is incomprehensible to me. Is he saying that we could know that, long ago, other species of hominins existed if not for ancient Homo sapiens who intentionally forgot? I'm lost. I read lots of novels and not an insignificant amount of poetry. I LOVE novels and I often LOVE poetry! But if this is poetry, then it might be Vogon poetry?
And here he's offering "the real meaning of the word human." It's, and he quotes, "an animal belonging to the genus Homo." But he includes no source for the quote. (My upcoming book's fact-checker would kindly ride my ass if I pulled something like that. I love her to death.) I'm guessing it is a quote from a dictionary.
It can only get better from here, right? Page 6-7 are next. To be continued...
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